Hydrodynamic actuating device for construction machines

ABSTRACT

A hydrodynamic actuating device has one prime mover, one torque converter and one rear-mounted transmission and is especially adequate for construction machines of wide range of motion such as wheel loaders. For limiting the maximum traction, one primary clutch ( 16 ) and one converter bridging clutch (WK) are both coordinated with the torque converter, which are disposed in series so as to be switchable via a single valve controlled by the transmission control with only a control pressure so that in all driving situations, first, the primary clutch ( 16 ) and thereafter the converter bridging clutch (WK) are closed.

The invention concerns a hydrodynamic actuating device for constructionmachines having one prime mover, one torque converter and onerear-mounted transmission, especially for construction machines havingwide range of motion, such as mobile cranes, wherein with the torqueconverter are coordinated one bridging clutch and one primary clutch forlimiting the maximum traction.

Hydrodynamic actuating devices consisting of one prime mover, one torqueconverter and one rear-mounted transmission have been used for a longtime in a multiplicity of different vehicles; the rear-mountedtransmission being mostly designed as reversing power shift transmissionin the case of construction machines. In a transmission of this kind,one power shift clutch is respectively provided for the forward gear andfor the reverse gear.

One example of a reversing transmission switchable under load which hasone hydrodynamic torque converter, one input shaft and one output shaft,one reversing set and gear clutches has been disclosed in theApplicant's DE A 198 46 955. This is a reversing transmission,especially suited for industrial lift trucks but also utilizable as aninput assembly of a multi-step reversing transmission so as to beadequate for other construction machines like wheel loaders.

Power shiftable reversing transmissions have a series of advantages.They have compact construction and are comfortable to switch. Inaddition, the hydraulically actuatable gear clutches can be switched bymodulating the switching pressure so that a controlled transfer of loadis ensured. In certain construction machines an in fork lift trucks,together with the reversing operation, other conditions are important asstarting off, inching and braking, for example.

For construction machines having wide range of motion, such as mobilecranes, one converter bridging clutch is installed in the torqueconverter and one stator freewheel is coordinated with the torqueconverter. The converter bridging clutch is designed so that at lowtraction requirements when no torque conversion is needed, it is closedin order to improve the degree of efficiency of the drive train.

With the hydrodynamic actuating devices described above, the maximumtraction cannot be changed, especially not limited, since the tractionin the stall point, i.e., when the output is stationary, depends only onthe rotational speed of the prime mover. Under full load, the torqueconverter absorbs the maximum power for the drive system and converts aconsiderable amount of that in the oil to heat. In order that thehydraulic pump for the working actuating device can produce highconveying capacity, the prime mover has to be kept at high rotationalspeeds.

To limit the traction of such a hydrodynamic actuating device at highrotational speed of the prime mover, there are two possibilities. Oneconsists in rear-mounting one secondary clutch on the torque converter,such as a directional clutch or providing a primary clutch between primemover and torque converter (impeller of the torque converter).

For reasons of energy, one primary clutch is to be preferred to asecondary clutch. It has to be taken into consideration here that it isa secondary clutch and not a primary clutch which has to transmit atorque higher by the converter ratio.

A slipping clutch for traction limitation also serves to reduce thepower that the torque converter absorbs. In construction machines, it isoften necessary to simultaneously actuate the drive system and one oilpump dependent on the prime mover for driving the working hydraulicsystem and, at the same time, guide the power precisely to where it isneeded.

The Applicant has produced so-called ergo-power transmissions withergo-inch function which have a secondary clutch with which the tractionis to be controlled to a small extent by way of a slipping directionalclutch.

Power shift clutches, however, are not able to produce high switchingcapacities for a long time such as those particularly needed for wheelloaders. Therefore, a traction limitation function is ruled out.

A hydrodynamic actuating device with a torque converter in which oneprimary clutch and one converter bridging clutch are integrated has beenproposed by the Caterpillar firm. For the control thereof two controlvalves are required which are independent of each other. The controlelectronics needed for their control must accordingly have two analogexits. The clutches integrated in a torque converter are, in addition,affected with the disadvantage that the converter inner pressurefluctuates strongly, can only be measured with difficulties and actsonly upon one side of the respective switch piston of the primary clutchor of the converter bridging clutch. Furthermore, the converter innerpressure depends, to a great extent, on the driving rotational speed,the temperature and the characteristic line of the usually providedconverter safety valve.

The problem on which the invention is based is to provide a hydrodynamicactuating device for construction machines of wide range of motion,especially a wheel loader, in which the traction at high rotationalspeed of the prime mover can be easily and reliably limited.

On the basis of a hydrodynamic actuating device having one prime mover,one torque converter and one rear-mounted transmission of the kindspecified above, said problem is solved with the features of thecharacteristic part of claim 1.

Advantageous developments are described in the sub-claims.

According to the invention, it is, therefore, provided that theconverter bridging clutch and the primary clutch be disposed in seriesso that they can be switched via a single valve controllable by thetransmission control with only one control pressure and this in a mannersuch that in all driving conditions, first, the primary clutch andthereafter the converter bridging clutch are closed.

The switching in series of both clutches provided, according to theinvention, is obtained by correspondingly dimensioning the piston recoilsprings and/or by adequate design of the piston surfaces.

It is especially advantageous that the two clutches be located in theinterior of the rear-mounted transmission. The advantage attained isthat the control of the clutches is entirely independent of the innerpressure predominant in the converter. It is also easily possible toinstall the two clutches either in parallel or superposed.

The invention is explained in detail herebelow with reference to thedrawing where two advantageous embodiments are shown as follows:

FIG. 1 is a diagrammatic section through the first illustration of aninventive hydrodynamic actuating device;

FIG. 2 is a diagram to make clear the switching in series of the twoclutches; and

FIG. 3 is a second illustration of an inventive hydrodynamic actuatingdevice.

In the schematically shown hydrodynamic actuating device of FIG. 1, theprime mover 14 of a motor vehicle on which one impeller torque converter2 is rear-mounted, the turbine 5 and the stator 6 and one freewheel 7being coordinated with the stator.

On the torque converter is rear-mounted one transmission the housing 8and the input shaft 1. This transmission is advantageously a reversingpower shift transmission known per se and well known to the expert andis not described in detail here. This transmission, which is usuallyprovided with one power shift clutch for the forward gear and thereverse gear, is preferably used in construction machines.

To make possible using the hydrodynamic actuating device also inconstruction machines having wide range of motion, especially in mobilecranes, with the torque converter is coordinated one bridging clutch WKwhich under low traction requirements when a torque conversion is notneeded, is closed in order thereby to improve the efficiency of thedrive train.

If the converter bridging clutch WK, as is usual in hydrodynamicactuating devices for construction machines known from the prior art, isinstalled in the torque converter, a limitation of the maximum tractionto a value below 100% is not possible. In the stall point, that is, whenthe output is stationary, the traction is dependent only on therotational speed of the prime mover. In case of full load, the maximumdrive capacity is inserted in the torque converter and in the oilconverted to heat. In order that the working hydraulic pump 15 canproduce high conveying capacity, the prime mover 14 must operate at ahigh rotational speed.

According to the invention, to now limit the traction at high rotationalspeed of the engine, one primary clutch 16 is provided which, togetherwith the converter bridging clutch WK, is switched with only one controlpressure. In this case, only one control valve is required and also onlyone analog exit to the appertaining control electronic system is to beprovided. The driving conditions are always such that, first, theprimary clutch 16 and thereafter the converter bridging clutch WK isclosed.

To this end, the piston 10 of the primary clutch 16 and the piston 11 ofthe converter bridging clutch WK are designed so that as the controlpressure P_(sys) increases, the primary clutch 16 first transmits torquewhile the converter bridging clutch WK is still open. When the controlpressure further increases, after the primary clutch 16 the converterbridging clutch WK also closes and transmits torque. This switching inseries of both clutches which is obtained by adequate dimensioning ofthe recoil spring 12 for the piston 10 of the primary clutch 16 and therecoil spring 13 for the piston 11 of the converter bridging clutch WKcombine with the respective piston surfaces is shown in FIG. 2 by thefunction T=f(P). In the embodiment chosen after applying the controlpressure P_(sys) the primary clutch 16 is first closed and, uponreaching a higher control pressure of 9 bar, the converter bridgingclutch WK is closed.

It is of special advantage when, as shown in FIGS. 1 and 3, the twoclutches are displaced into the interior of the rear-mountedtransmission, since thereby the control of the clutches is independentof the inner pressure and the changes that prevail in the converter.

In the embodiment shown in FIG. 1, the primary clutch 16 and theconverter bridging clutch WK are disposed in parallel in the interior ofthe housing 8. The piston carrier 3 is connected with the impeller 2 ofthe torque converter, the disc carrier 4 is connected with the pistoncarrier 3 and one output gear 9 is connected with the turbine wheel 5,which makes a further power flow possible to the stepped transmissionthat follows.

In the embodiment shown in FIG. 3, where the same parts are providedwith the same reference numerals, the two clutches are disposed not inparallel but superposed.

In the primary clutch 16, according to the invention, the inner discsare connected with the input shaft 1 and the outer discs with theimpeller 2. Between the two clutch pistons 10, 11 lies the pressurizedoil supply. The pressurized oil is fed to the piston space via a centralaperture (not shown), in the input shaft 1 and, via piston rings (notshown) between input shaft 1 and the impeller shaft.

REFERENCE NUMERALS

-   1 input shaft 10 piston of primary clutch 16-   2 impeller torque converter 11 piston of converter bridging clutch    wk-   3 piston carrier 12 recoil spring for pistons of the primary-   4 disc carrier clutch 16-   5 turbine wheel 13 recoil spring for pistons of wk-   6 stator 14 prime mover-   7 freewheel 15 pump drive for hydraulic system-   8 housing 16 primary clutch-   9 output wheel WK converter bridging clutch

1-8. (canceled)
 9. A hydrodynamic actuating device having one primarymover, one torque converter and one rear-mounted transmission, forconstruction machines having a wide range of motion, one bridging clutch(wk) and one primary clutch (16) are coordinated with the torqueconverter for limiting maximum traction, the primary clutch (16) and theconverter bridging clutch (wk) are disposed in series so as to beswitchable via a single valve controlled by a transmission control withonly one control pressure so that in all driving situations first theprimary clutch (16) and thereafter the converter bridging clutch (WK)are closed.
 10. The hydrodynamic actuating device according to claim 9,wherein the switching in series of the primary clutch (16) and of theconverter bridging clutch (WK) is produced by adequately dimensioningpiston recoil springs (12, 13) and by adequate design of surfaces ofpistons (10,11).
 11. The hydrodynamic actuating device according toclaim 9, wherein the torque converter is connected with the rear-mountedtransmission via one stator freewheel (7).
 12. The hydrodynamicactuating device according to claim 9, wherein both the primary clutch(16) and the converter bridging clutch (WK) are located in an interiorof the rear-mounted transmission.
 13. The hydrodynamic actuating deviceaccording to claim 12, wherein the primary clutch (16) and the converterbridging clutch (WK) are disposed in parallel.
 14. The hydrodynamicactuating device according to claim 12, wherein the primary clutch (16)and the converter bridging clutch (WK) are disposed superposed.
 15. Thehydrodynamic actuating device according to claim 9, wherein inner discsof the primary clutch (16) are connected with an input shaft (1) andouter discs of the primary clutch (16) are connected with an impeller(2) of the torque converter.
 16. The hydrodynamic actuating deviceaccording to claim 9, wherein inner discs of the converter bridgingclutch (WK) are connected with a turbine wheel (5) of the torqueconverter and outer discs are connected with an impeller (2) of thetorque converter.